In homeotic mutants, the identity of one body structure has been changed into another. (a) Normal fly with one pair of forewings on the second thoracic segment and one pair of small hind wings on the third thoracic segment. (b) Triple mutant for three mutations in the Ultrabithorax gene. Ubx function is lost in the posterior thorax, which causes the development of forewings in place of the hind wings. (c) Antennapedia mutant in which the antennae are transformed into legs.
[Sean Carroll.]